Less invasive surgery techniques are usually more desirable than more invasive techniques because the patient suffers less trauma, suffers fewer side effects, and heals quicker. For a given pathology, endoscopic surgery is often less invasive than other surgical options. In endoscopic surgery, a surgeon guides a relatively small endoscope configured as a probe to a target region of a body part. The endoscope generates live video images of anatomy encountered at the tip of the probe, and the surgeon uses these video images as an aid in guiding the probe to the target region. Similarly, a guided microscope can be employed to show where a variety of instruments should be applied. Once the probe has been guided to the target, a variety of surgical techniques may then be performed at the target region.
However, endoscopic surgery has conventionally been considered too dangerous where few distinctive visual features are available within a subject body part. When few distinctive visual features are available, the surgeon risks becoming disoriented while guiding the probe to the target region. This disorientation may cause the surgeon to inflict extensive trauma on the patient while failing to reach the target region. Since few distinctive visual features are found in the interior of many internal organs, such as the brain, many pathologies have not been successfully operated upon endoscopically.
Endoscopic surgery within the brain has often been considered exceptionally risky because a path followed by a probe in traversing from outside the body to a target region, for example a tumor, should avoid critical or eloquent areas of the brain to the maximum extent possible to prevent permanent brain damage. Consequently, not only does a probe or needle need to be guided to a target region, but the probe should be guided to the target region over a specific route or trajectory. Disorientation and a resulting deviation from a specific trajectory may lead to severe consequences even when the target region is successfully reached.
Various systems and techniques have been devised to let a surgeon know the location of a surgical instrument within a body even though few visual clues may be available. For example, various framed and frameless stereotactic surgical techniques incorporate systems for informing a surgeon of an instrument position. When such position information is accurate, it may help a surgeon find a target region. However, mere position information fails to inform a surgeon about whether an instrument is on a specific trajectory, and such information fails to inform a surgeon of actions needed to cause an instrument to more closely approach a specific trajectory. Consequently, a high risk of disorientation still remains when limited visual clues are present.
In addition, various systems present tomogram images in combination with surgical instrument position information. For example, during surgery a surgical instrument's position may be superimposed or otherwise indicated on a tomogram which is viewable by the surgeon. These tomogram-based systems attempt to better inform a surgeon of whether an instrument is positioned as desired because a surgeon can view instrument position relative to an overall tomogram image.
However, tomograms represent anatomy at a past point in time and in a situation where the anatomy is not being influenced by the surgery itself. Tomograms fail to reveal actual anatomy at the instant of surgery and under the influence of surgery. Consequently, tomograms often fail to provide accurate anatomical renditions existing during surgery, and relative position information indicated on tomograms may not be accurate. Moreover, even if a tomogram-based system happens to accurately portray relative instrument position, nothing informs a surgeon about whether an instrument's position is consistent with a specific trajectory or about actions needed to cause an instrument to more closely achieve a specific trajectory.
Still other systems attempt to perform extensive 3-D computer enhancement and reconstruction of tomogram images during surgery in response to instrument position information in an attempt to better allow a surgeon to visualize instrument orientation and anatomy traversed by the surgical instrument. However, no amount of computer reconstruction can make tomogram images taken at a past point in time under non-surgical conditions to accurately portray anatomy under the influence of surgery. Moreover, complex 3-D computer analysis of tomogram images requires extensive computing power, causing a time lag between the actual instrument positioning and the resulting enhanced or reconstructed images. Such systems merely react to actions already taken by a surgeon and fail to adequately inform a surgeon of what future actions are needed to guide an instrument along a specific trajectory to a target region.